Comparison of several innovative bridge cable surface modifications

Over the last two decades, several bridge cable manufacturers have introduced surface modifications on the high-density polyethylene (HDPE) sheathing that is installed for the protection of inner cable strands or wires. The modifications are based on research undertaken predominantly in Europe and Japan, with two different prevailing systems: HDPE tubing fitted with helical fillets and tubing with pattern-indented surfaces.

In the US and Europe, helical fillets dominate, whilst pattern indented sur-faces are more common in Asia, particularly for long-span cable-stayed bridges. Research into the effectiveness of helical fillets and pattern-indented surfaces has shown that, be-sides their purported ability to suppress rain-wind induced vibrations, they also modestly reduce drag forces at design wind velocities.

This is of particular interest to bridge designers, as wind on stay planes of long-span bridges can now produce more than 50% of the overall horizontal load on the bridge (Gimsing and Georgakis, 2012). Recently, the authors presented a comprehensive comparative study of the aerodynamic performance of these existing cable surface modifications (Kleissl and Georgakis, 2011, 2012).

The comparison helped to eliminate uncertainties in previous studies, due to the fact that several researchers, in different facilities, with varying wind-tunnel flow characteristics and performance, have developed each separately. During the study, the authors were able to docu-ment the performance advantages of each of the modifications, but often not to the levels that have been commonly reported.

Therefore, similarly to Yagi et al. (2011), several new surface modifications are proposed here-with, in an attempt to combine and enhance the performance advantages of each of the existing modi-fications. Each of the proposed modifications was investigated through wind tunnel testing. The re-sulting mean static force coefficients were obtained from wind tunnel tests, with the cables positioned normal to the wind, and were used as “gateway” criteria for the subsequent investigation of rain rivulet suppression.